The present invention relates to a novel positive-working photoresist composition or, more particularly, to a high-sensitivity positive-working photoresist composition capable of giving a finely patterned resist layer in a high resolution and excellent in the cross sectional profile of the patterned layer and heat resistance with an excellent characteristic of focusing depth latitude.
As is known, the photolithographic patterning is a well established technology in the process for the manufacture of semiconductor devices such as ICs, LSIs and the like and liquid-crystal devices such as liquid crystal display panels and the like. The photolithographic patterning work is conducted by first forming a layer of a so-called photoresist composition which is pattern-wise exposed to light to form a latent image of the pattern followed by development. Of the two types of photoresist compositions including positive-working and negative-working ones, the positive-working photoresist compositions are preferred in most cases to the negative-working ones and the essential ingredients in a typical positive-working photoresist composition under practical use include an alkali-soluble resin as a film-forming ingredient and a quinone diazide group-containing compound as a photosensitive ingredient.
The alkali-soluble resin as a film-forming ingredient in a positive-working photoresist composition most widely used in practical applications is a novolac resin in respect of the advantageous properties thereof that the resin is soluble in an alkaline aqueous solution as a developer solution without swelling to exhibit excellent developability and the resist layer formed therefrom has excellent heat resistance to withstand plasma etching with the patterned resist layer as an etching mask.
The quinone diazide group-containing compound as the photosensitive ingredient is very unique because the compound in itself has an activity to suppress the alkali solubility of the novolac resin while, when irradiated pattern-wise with actinic rays including electromagnetic waves such as ultraviolet light, e.g., g-line and i-line, and far-ultraviolet light, e.g., excimer laser beams, and corpuscular rays for pattern-wise scanning such as electron beams, the quinone diazide group-containing compound per se is converted into an alkali-soluble form along with promotion of the alkali-solubility of the novolac resin. Thus, a great number of positive-working photoresist compositions comprising a quinone diazide group-containing compound and an alkali-soluble novolac resin and capable of exhibiting a great change in the properties by exposure to actinic rays such as electromagnetic waves and corpuscular rays have been developed and brought under practical applications (see, for example, U.S. Pat. No. 4,377,631, Japanese Patent Kokai No. 62-35349, Japanese Patent Kokai No. 1-142548, Japanese Patent Kokai No. 1-179147 and Japanese Patent Publication No. 3-4897).
Along with the increase year by year in the degree of integration in the semiconductor devices and liquid crystal devices in recent years, the accuracy required in the photolithographic patterning work is so high as to have a fineness in the order of submicrons, half microns or even finer in the manufacture of, for example, VLSIs. Accordingly, the positive-working photoresist composition used therefor must satisfy several requirements that the composition can give a patterned resist layer having high resolution of the patterned images, that the patterned resist layer has an excellently orthogonal cross sectional profile and excellent heat resistance not to cause thermal deformation in the dry etching or the post-exposure baking, i.e. heat treatment after exposure to actinic rays and before development, and that the sensitivity thereof is high in respect of the productivity along with an excellent focusing depth latitude so as to facilitate reproduction of the resist pattern with high fidelity to the mask pattern without being affected by a level difference on the substrate surface.
As a means to accomplish the above mentioned requirements in the performance of a positive-working photoresist composition, various attempts and proposals have been made for the improvement of the performance of the alkali-soluble resin as the film-forming ingredient therein. For example, Japanese Patent Kokai No. 2-867 proposes a positive-working photoresist composition in which the film-forming resin is a resin blend consisting of a first resin which is a condensation product of 2,5-xylenol, m-cresol and p-cresol with an aqueous formaldehyde solution and a second resin which is a condensation product of 3,5-xylenol, m-cresol and p-cresol with an aqueous formaldehyde solution. These resin blends are defective in the poor resolution and form of the contact holes as a consequence of the fact that each of the constituent resins is a xylenol-cresol novolac resin and they are also not satisfactory in respect of the resolution as the most important factor to influence on the working accuracy of ultra-fine patterning in recent years and in respect of the sensitivity to accomplish a high throughput of the products.
Further, Japanese Patent Kokai No. 2-108054 proposes a positive-working photoresist composition of which the film-forming ingredient is a resin blend consisting of a high molecular-weight novolac resin obtained by the condensation reaction of m-cresol, 2,3,5-trimethyl phenol and, optionally, p-cresol with an aldehyde compound having a weight-average molecular weight of 4000 to 20000 and a low molecular-weight novolac resin having a weight-average molecular weight of 200 to 2000. Japanese Patent Kokai No. 3-228059 also proposes a photoresist composition similar to that described above. Although these photoresist compositions have improved heat resistance and photosensitivity as a consequence of blending of two different novolac resins, one, having a relatively large weight-average molecular weight and, the other, having a small weight-average molecular weight, they are still insufficient in respect of the resolution as an essential requirement to obtain a high patterning accuracy in the ultrafine patterning works in recent years and photosensitivity to accomplish a high throughput of the products.
On the other hand, it would be a possible approach to improve the resolution in the photolithographic patterning by increasing the numerical aperture of the lens system in the light-exposure apparatus but a large numerical aperture of the lens system is incompatible with the requirement for a good focusing depth latitude so that such a means is hardly applicable when the surface of the resist layer has a relatively large level difference. It is eagerly desired therefore to develop a positive-working photoresist composition which is safe from the problem of a decrease in the focusing depth even with an increased numerical aperture of the lens system while none of the prior art positive-working photoresist compositions meets such a requirement.